Swash plate rotary machines



April 28, 1964 D. FIRTH ETAL.

swAsH PLATE ROTARY MACHINES 3 Sheets-Sheet 1 Filed May 22, 1961 April 28, 1964 D. FIRTH ETAL. 3,130,584

swAsH PLATE ROTARY MACHINES Fileduay 22, 1961 3 Sheets-Sheet 2 April 2s, 1964 D. HRTH ETAL 3,130,684

SWASH PLATE ROTARY MACHINES Filed May 22, 1961 3 Sheets-Sheet 3 w v l o M o Q u l l |I I "f. l 1

United States Patent 3,130,684 SWASH PLATE RTARY MACHENES Donald Firth and Roger Harvey Yorke Hancock, both of East Kiibride, Glasgow, Scotland, assignors to Council for Scientilic and industrial Research, London, England, a corporation of the United Kingdom Filed May 22, 1961, Ser. No. 111,724 Claims priority, application Great Britain May 25, 1960 1li Claims. (Q1. 10S-162) vapplications demand both stability in the maintenance of a chosen speed and flexibility of speed control.

Variations of the speed of a motor can be achieved in two ways-variations of the rate of supply of working fluid and variations of the working stroke of the pistons. In swash plate pumps and motors, both requirements can be satisfied by adjustment of the angle of tilt of the swash plate. Provision for such adjustment, however, may lead to loss of rigidity of the swash plate, which then becomes subject to vibration during operation of -the machine, with resultant iluctuations in output and increased noise, both of which may reach unacceptable levels.

The present invention accordingly aims at providing for ready adjustment of the angle of tilt of the swash plate while avoiding or minimising any loss of rigidity.

According to the invention there is provided a swash plate rotary machine having its swash plate mounted for tilting about a pivot axis and means for clamping the swash plate at a desired angle of tilt comprising two or more struts engaged between abutment members and the swash plate at points located around the swash plate adjacent its periphery and remote from the pivot axis, the struts being adapted to maintain a state of stress in the swash plate.

Preferably, a pair of struts is provided engaging the swash plate at two points located diametrically opposite keach other on a line at right angles to the pivot axis.

Advantageously, each strut is adjustable for effective length in order to determine the angle of tilt.

Stressing of the swash plate may be achieved mechanically, by means such as captive rotatable nuts, sleeves or the like, or by hydraulic means, each strut being constituted by an hydraulic ram or plunger. Automatic .valve means may be associated with at least one such ram or plunger for maintaining the position of adjust- Vment `of the swash plate.

Preferred embodiments of the invention will now be particularly described, by way of illustration only, with reference to the accompanying drawings in which:

FIGURE 1 is a fragmentary longitudinal section (partly in elevation) through a rotary swash plate pump having hydraulic struts'for adjusting and maintaining the angle of tilt of the swash plate, and

FIGURE 2 is a similar view of a pump having a mechanical arrangement of strut, and

FIGURE 3 is a sectional view at right angles to the section of FIGURE 2.

The drawings depict swash plate pumps constructed ice and drawings of co-pending patent applications Nos. 22,334, tiled April 14, 1960, and 83,089, iiled January 16, 1961. If desired, the pumps may be employed without structural modification, as hydraulic motors.

Referring rst to FIGURE l of the drawings, the pump illustrated has end-covers l, 2 carrying bearings 4, 5 respectively for the pump shaft 6. This shaft carries a cylinder block 8, and passes through a swash plate 12 whose angle of inclination determines the output of the pump. The swash plate is mounted on trunnions 13 for pivotal adjustment about an axis O which is offset from the axis of the shaft 6 and lies in a direction at right angles thereto. l

The cylinder block 8 contains a plurality of cylinders with pistons 11 (only one of which is shown in the drawing, for the sake of clarity) reciprocable therein. Each piston carries a slipper 14 which bears against an annular slipper plate 15 mounted on the swash plate 12. The end-cover 2 has inlet and outlet ports with which the cylinders in the block 8 communicate in turn as the block rotates and the pistons 11 reciprocate under control of the swash plate. Y

The swash plate 12 is anchored in the required position of angular adjustment by means of a pair of struts 69, 70 having hemispherical ends 71 which rest in respective hemispherical sockets 72 on the swash plate 12 and 73 in abutment pads 74, 75 on the inner ends of respective hydraulic pistons or rams 76, 77. These pistons or rams work in respective cylinder blocks 78, 79 located in sockets 89 in the end cover 2 and secured therein by bolts 81. The sockets 72 lie on a common diameter of the swash plate 12 at right angles to the axis O so that they are removed angularly as far as possible from the axis of tilt of the swash plate and thus offer the greatest control moment about this axis.

In the above-described arrangement the ram 76 is a control ram and the ram 77 is a reaction thrust ram, the latter being of slightly smaller effective diameter than the former. i

The control ram 76 works in a bore S2 in the cylinder block 78 and has axially spaced outer and inner lands 83, 84 between which is an annular relief 85. Inwards of the inner land 84 the ram is also relieved as shown at 86. A main oil pressure inlet port 90 opens into the relief 85 between the lands 83, 84. Each relief 85, 86 communicates through a respective port 87, 88 with an axial valve chamber 89, the port 67 being radial and the port 88 being inclined. The transfer ports open into the valve chamber on opposite sides of an annular groove 91. This groove breaks into a channel 92 which runs parallel to the valve chamber and communicates with a second or inner annular groove 93 near the abutment pad '74 which closes the inner end of the valve chamber 89. The outer end of the channel 92 is in open communication with the cylinder bore 82 behind the control ram 76.

In the chamber 39 lies a piston valve 94 having outer,

middle, and inner lands 95, 96, 97 respectively. The

Vdrain port 101 with the annular relief 86 around the inner end of the control ram 76. The radial play in the mounting of the piston valve 94 on the control rod 98 is sutlicient to allow it to align itself accurately in the valve chamber 89 without constraint from the rod, but the valve 94 is axially located on the control rod 98 by means of a collar 102 fixed on the rod and against which the valve is urged by a helical compression spring 103 which is compressed between the inner end of the valve and a washer held in place by a nut 104 threaded on the control rod 98. Any oil which leaks along the control rod 98 to the gland 99 or into the relief 86 around the inner end of the control ram 76 is drained off through ducts 105, 106 and a drain channel 107.

The reaction thrust ram 77 is a plain piston without ports or valves working in a plain bore 108 which is connected at a port 109 through a constriction 110 to the same supply 111 of high pressure oil as that which feeds, through another constriction 112, the control ram 76, through its inlet port 90.

The system operates as follows:

Oil under pressure is' fed from the supply 111 to the inlet ports 90 and 109 of the two rams. In the absence of any other checks or controls, this would result in the progressive tilting of the swash plate 12 to its maximum angle, due to the larger effective piston area of the control ram 76 than of the reaction ram 77. The valve 94, however, prevents this from happening.

The control valve 94 is axially positioned by the control rod 98 to correspond with the desired angle of tilt of the swash plate 12. With the parts in the positions shown in the drawings, the swash plate 12 is in its neutral position of zero tilt in which no pumping takes place. In order to tilt it, therefore, the control ram 76 must move to the right. Oil fed to the inlet port 90 :fills the annular relief space 85, the transfer port 87, and the annular space between the outer and middle lands 95, 96 of the control valve 94. The middle land 96, however, closes the groove 91, so no oil can leave this part of the unit.

If now the control valve 94 is moved by the control rod 98 to the right, the land 96 immediately uncoversl the outer-ie. left-hand-edge of the groove 91, and oil under pressure passes into the channel 92, filling the inner end of the valve chamber 89 and the outer ends of both this chamber and the ram bore 82. The resulting thrust to the right on the end face of the control ram 76 in the ram bore 82 causes the ram 76 to move to the right, tilting the swash plate 12 against the reaction thrust provided by the ram 77, which is thereby forced outwards. Oil in the cylinder bore 108 behind this ram is transferred through the constriction 110, 112 in series to the inlet port 90 of the control ram.

As the control ram 76 moves inwards, the groove 91 gradually becomes closed by the middle land 96 of the control valve 94 until it eventually becomes shut off. At this point, the supply of oil to the cylinder space behind (i.e. to the left of) the ram 76 ceases and the ram cannot travel any further. The oil behind the ram is now trapped and forms a lock against any tendency for the swash plate 12 to be returned to its zero tilt positionfor example, by a resultant mechanical thrust from the pump pistons.

The control valve 94 is hydraulically balanced under these conditions, and can therefore be moved by the control rod 98 to a new position. If it is retracted-ie. moved to the left in the drawing-the middle land 96 immediately uncovers the inner (right-hand) edge of the groove 91 and places the channel 92 in communication with the oblique transfer port 88. Oil thus flows to exhaust via the inner annular relief 86, port 106, and exhaust channel 107, the thrust of the reaction thrust ram 77 causing the swash plate 12 to force the control ram 76 back until it overtakes the control valve 94 and the groove 91 is again sealed by the middle land 96. Equilibrium conditions are then restored and the swash plate is again locked, the control valve 94 automatically maintaining the required angle of tilt of the swash plate.

The opposing thrusts of the two rams 76, 77 maintain a state of stress in the swash plate 12 which assists in reducing vibration from the cyclic unbalance of the reactions from the pump cylinders. lf these vibration forces reach sufcient magnitude to cause displacement of the control ram 76 and reactionthrust ram 77, oil will tend to be transferred between the two cylinder bores 82 and 108, and the two constrictions 110, 112 are in series in the interconnecting circuit to act as dampers. The system is thus inherently stable to maintain the swash plate 12 in its position of adjustment and thus to promote smooth operation of the pump.

In order to reduce any tendency of the control ram 76 to hunt about its preset position, a constriction 113 is preferably inserted in the channel 92 to damp the oil flow through the valve 94.

The source of oil pressure at 111 is preferably the output or line pressure of the machinewhether the latter is acting as a pump or as a motor-although an independent supply of oil under pressure may be used if preferred. The control rod 98 may be manually operated, or it can be linked to an automatic controller responsive to an external condition such as output pressure of a pump or output speed or torque of a motor.

In the alternative construction shown in FIGURES 2 and 3, the pump, as before, has end-covers 1, 2 carrying bearings 4, 5 for the pump shaft 6 which carries a cylinder block 8 `and passes through a swash plate 12 whose angle of inclination determines the output of the pump. The swash plate is mounted on trurnnions 13 for pivotal adjustment about an axis which lies in a direction at right angles to the axis of the shaft 6. rIlhe block 8 contains a plurality of pistons 11 (only one being shown in FIGURE 2 and only two in FIGURE 3, for clarity of illustration) and each piston has Ea slipper v14 bearing yagainst a slipper plate 15 on the swash plate. In this alternative construction, the hydraulic rams 76, 77 are replaced by mechanical jacks The struts `69, 70 of FIGURE l have their counterparts in similarly acting struts 169, 170 in FIG- URE. 2, the latter, however, having their hemispherical ends 171 resting in complementary sockets formed in bearing pads 172 which rest against the -at surface of the swash plate `12.

Each strut 169, 170iy passes through a tubular guide pillar wihich is screwed into the end cover 2 of the pump (or motor). Each strut isv threaded into the outer (leftlhand) end fof its tubular guide as shown at 121, and the outer projecting portion of the screw thread on the strut carries a tubular lock nut 122 which is accommodated iny Ia plain extension 1213- of the threaded socket which receives the guide pillar 170. The outer end of each nut 122 is castellalted lat 124 for engagement by a tubular key.

4Each strut 169, 170 has its outer end 125 of reduced diameter and terminating in a standard hexagon head 126 for engagement by Ka Spanner, this end of the strut being shielded by a hollow cap nut 127. By removing the cap nuts and slackening olf the tubular lock nuts 122, the struts 169, 17 0 can be screwed in or out in opposite senses to adjust the angle of tilt of the swash plate 12, the latter being finally clamped in fthe desired position by the opposing thrusts of the stnuts.

If desired, the struts 169, may be splined in their guide pillars 120 in place of the threaded formations at 121 and their outer ends y125 may be threaded to engage captive nuts (not shown) which are driven from a common shaft to adjust the struts in opposition. The shaft may then be operated by an 'automatic controller. In onder to ensure the maintenance of the necessary compressive stress in the struts 169, 170` and `at the same time allow for manufacturing tolerances and wear in the threaded parts, the dri-ve to each captive nut may be transmitted through a torque limiting clutch from a conventionall form of `differential gear.

In a further 'alternative construction also not illustrated in the drawings, the struts 169, 170 may be adjusted by means of cams in place of the captive nuts, the earn followers consisting, if desired, Ior hydraulic plungers whose hydraulic circuits are fed at constant pressure to maintain equal stresses in the struts.

In all forms of the invention, the swash plate 12 is preloaded to an extent suliicient to overcome the lluctuating reaction thrust exerted thereon by the cyclic variation in the number of pump or motor cylinders which are operating at maximum load during each revolution of the cylinder block. This pre-loading also results in a higher bearing pressure on the swash plate trunnions which produces higher frictional resistance to oscillation of the swash plate, and hence increased damping action is obtained which promotes smoother and quieter running of the machine.

Although in the foregoing description two struts 69, 70 or 169', 170 have been shown placed at opposite ends of a diameter of the swash plate 12., it is to be understood that more than two struts m-ay be equiangularly spaced around the |axis of the shaft 6.

We claim:

l. In a swash plate rotary machine, the combination of a tiltable swash plate mounted between two pivots, a pair of struts hafving ends engaging diametrically opposite parts of the swash plate adjacent its periphery and on a line at right angles to the pivot axis, abutment members engaged by the struts at their other ends, hydraulic rams carrying said abutment members, cylinders containing said rams each having a pressure-Huid inlet and containing a working space at one en-d ot the ram, a pressurefluid interconnection between said inlets, a pressure-huid supply connection to said interconnection, a damping constriction between the supply connection and each inlet, a piston valve reciprocable within a bore in one of the rams, and ports connecting said bore with the pressure-fluid inlet into the cylinder, with the cylinder working space and with an exhaust outlet, said piston valve being moviable to ditte-rent positions connecting the pressure-iluid inlet with the cylinder lworking space, connecting the cylinder working space with the exhaust outlet and sealing the cylinder working space.

2. The combination according to claim l wherein the piston valve has a control land which normally closes the port connecting said bore with the cylinder working space and the ports to the pressure fluid inlet and the exhaust outlet are disposed on opposite sides of said port to the working space.

3. The combination according to claim 2 wherein the port to the pressure huid inlet is in a position between the cylinder working space and the port thereto, whereby movement of the piston valve opening the port to the working space results in movement of the ram in a direction to restore the piston valve to its normal position relative to the ram.

4. 'Ilhe combination according to claim 3 wherein the piston valve has two lands spaced axially beyond the ports to the pressure fluid inlet and the exhaust outlet.

'5. 'Ilhe combination according to claim 4 wherein said port to the pressure fluid inlet communicates with a recess on the outside of the piston vlalve, the pressure-Huid inlet opening into said recess.

6. A swash plate rotary machine comprising a swash plate, a rotatable cylinder block, a plurality of pistons reciprocable in cylinders of the cylinder block under control of the swash plate, a stationary port block having inlet and outlet ports cooperating with ports in the cylin- Yder block leading to the cylinders therein, pivots supporting the swash plate, the pivot axis being transverse to the axis of rotation of the cylinder block, a plurality of struts each of 'which at one end engages the swash plate at a point adjacent its periphery and remote from said pivot axis and at the other end bears against an abutment member, and loading means acting on the struts to stress the swash plate, said loading means comprising hydraulic rams carrying said `abutment members, cylinders containing said rams each i' eving a pressure-huid inlet and containing a working space at one end ot the ram, a pressureiluid interconnection between said inlets, a pressure-huid supply connect-ion to said interconnection, a damping constriction between the supply connection and each inlet, a piston valve reciprocable within a bore in one of the rams, and ports connecting said bore with the pressure-duid inlet into the cylinder, with the cylinder working space and an exhaust outlet, said piston valve being movable to different positions connecting the pressure-huid inlet with the cylinder working space, `connecting the cylinder working space with the exhaust outlet and sealing the cylinder working space.

7. In a swash plate rotary machine, the combination of a tiltable swash plate, hydraulic ram means engaging the swash plate at substantially diametrically opposite positions distant from the tilting axis, a common pressure fluid connection to sai-d ram means, pressure-huid interconnection -between said ram means into Which said common pressure-fluid connection opens, a damping constriction in said interconnection between said common pressure-duid connection and each ram means, rams in said ram means having different eiective areas exposed to pressure fluid, whereby one ram means exerts a lower pressure on the swash plate than the other ram means, a piston valve reciprocable within a bore in a ram of the last-mentioned ram means, a cylinder within which said ram reciprocates, said cylinder having a pressure fluid inlet communicating with said common pressure fluid connection and an exhaust outlet, Iand ports in the ram connecting the bore therein with the pressure-fluid inlet into the cylinder, with the cylinder working space and with the exhaust outlet from the cylinder, said piston valve being movable to different positions connecting the pressure-fluid inlet with the cylinder working space, connecting the cylinder working space with the exhaust outlet and sealing the cylinder lworking space and sai-d piston valve having a control land which normally closes the port connecting said bore with the cylinder working space, the ports to the pressure fluid inlet and the exhaust outlet being disposed on opposite sides of said port to the working space and the port to the pressure fluid inlet being in a position between the cylinder working space and the port thereto.

8. The combination according to claim 7 wherein a constriction is provided between the cylinder working space and the port thereto.

9. The combination according to claim 7, wherein a control rod is provided for moving the piston valve axially, said control rod passing with radial play through the piston valve.

l0. In a swash plate rotary machine, the combination of a tiltable swash plate, irst hydraulic ram means acting on the swash plate on one side of the tilting axis for tilting the swash plate in one direction, second hydraulic ram means acting on the swash plate on the other side of the tilting axis for tilting the swash plate in the opposite direction against the `action of the iirst ram means, said rst and second ram means acting von the swash plate at positions distant from the tilting axis, a pressure lluid interconnection between the iirst and second ram means, a pressure iluid supply connection to said interconnection iior supplying hydraulic fluid to both the first and lsecond ram means, Valve means in said interconnection between the pressure fluid supply connection and the second ram means for selectively vconnecting said second ram means to pressure and exhaust, said valve means comprising a follow-up valve having a part coupled to the swash plate to move therewith and a control member movable relatively to said part for selectively connecting the second ram means to pressure and exhaust, a iirst damping constriction in said interconnection between the pressure iiiuid supply connection and the rst ram means and a second damping constriction in said interconnection between the pressure iluid supply connection and said valve means.

(References on following page) "7 References Cited in the file of this patent 2,915,985 UNITED STATES PATENTS fg 1,794,946 Crain Mar. 3, 1931 I 2,265,314 Rose Dec. 9, 1941 55 2,409,185 Blasutta 001.15, 1946 812,927 2,696,189 Born et al Dec. 7, 1954 8 Budzich Dec. 8, 1959 Budzich Sept. 20, 196() Lambeck Aug. 28, 1962 FOREIGN PATENTS Great Britain May 6, 1959 

1. IN A SWASH PLATE ROTARY MACHINE, THE COMBINATION OF A TILTABLE SWASH PLATE MOUNTED BETWEEN TWO PIVOTS, A PAIR OF STRUTS HAVING ENDS ENGAGING DIAMETRICALLY OPPOSITE PARTS OF THE SWASH PLATE ADJACENT ITS PERIPHERY AND ON A LINE AT RIGHT ANGLES TO THE PIVOT AXIS, ABUTMENT MEMBERS ENGAGED BY THE STRUTS AT THEIR OTHER ENDS, HYDRAULIC RAMS CARRYING SAID ABUTMENT MEMBERS, CYLINDERS CONTAINING SAID RAMS EACH HAVING A PRESSURE-FLUID INLET AND CONTAINING A WORKING SPACE AT ONE END OF THE RAM, A PRESSUREFLUID INTERCONNECTION BETWEEN SAID INLETS, A PRESSURE-FLUID SUPPLY CONNECTION TO SAID INTERCONNECTION, A DAMPING 